The eye is basically a sphere 2.4 cm in diameter,
(a little less than one inch.)

Take a look at a one inch diameter plastic sphere
to see a model of the eye.

We'll start with exhibits progressing from the
Cornea to the retina.

Then we'll do some hands-on explorations including
a web guided cow's eye dissection.

Cornea and lens

The eye forms an image on the retina by bending
light, refracting light, through the cornea and the lens. Most of the
bending comes from the cornea, however, the lens makes an important
fine adjustment which sharpens the focus.

When you look at a small bright light often you
will see lines radiating from it, painters often show these lines
surrounding stars, see for example lines radiating from the Christmas
star. Here is an investigation of the source of those
lines.

After doing this activity you may begin to see why
we started our exploration of science with a study of perception. The
rays which you thought existed around a light bulb were not really
there but were the result of your perception.

Science Mulch

The cornea is made of a tough clear material. In humans
it has 5 layers. The living bottom layer is nourished by the
aqueous humor.

Iris and Pupil

The iris gives the eye its color. The iris expands
and contracts forming the pupil which controls the amount of light
entering the retina. Let's explore the pupil.

The vitreous humor is a gelatinous material that
fills the eye behind the lens and presses the retina up against the
back of the eye. Occasionally, the retina will hemorrhage so that red
blood cells and white blood cells leak out into the vitreous humor.
You can see these cells drifting about in your field of view when you
look at a clear blue sky.

The retina is where it's at! Here rods and cones
convert light into electrical signals. The human retina is built in a
strange way with the blood supply and the neurons in front of the
light sensitive cells. This allows us to look at our own retinal
blood supply.

When you come to the Exploratorium you must see an
exhibit titled, "Corpuscles of the Eye." This exhibit is too
expensive to build yourself. When you look into the eyepiece of what
looks like a small telescope you see many bright points of light
dancing across your field of view. They dance to a regular rhythm,
your heartbeat. The particular narrow band of blue light wavelengths
in this exhibit has been chosen to allow you to see the diffraction
pattern of red blood cells as they pulse through the blood supply in
front of your retina.

Another exhibit is named Macula, look at a disk of
light that alternates between purple and blue. In the center of the
blue light a dark shadowy shape may appear. This is the visual
appearance of the macula. Not everyone can see their macula, but
those who do report seeing disks, dandelions, and klingon bird of
prey spacecraft shadows. Notice that the size of the macula changes
as you approach and then go away from from the screen. The macula is
a fixed portion of the retina, near the fovea, but no one knows
exactly how it is made.

There are many more activities we could do but
this is a good time to take a break.

Break

Welcome back!

Now let's get a hands-on experience with an eye.
We'll do a cow's eye dissection. You can do this for real by calling
up your local slaughterhouse and arranging to get a cow's eye. Or you
can do this electronically at the Exploratorium's cow's eye
dissection site. Nothing beats the real thing though, so go for it!
Get a cow's eye and start exploring.